Porous Filamentous Nanocarbon And Method Of Forming The Same

ABSTRACT

There is provided a porous filamentous nanocarbon and a method for forming the same. A mesopore formed on an outer periphery of the porous filamentous nanocarbon is a tunnel-like pore which is formed along the arrangement direction of the carbon hexagonal plane from the outer periphery toward a fiber axis. The porous filamentous nanocarbon is fabricated by selectively removing the carbon hexagonal plane constituting the filamentous nanocarbon through gasification in virtue of a catalyst, after highly dispersing Fe, Ni, Co, Pt, etc., of which size is 2-30 nm, on the surface of the filamentous nanocarbon. That is, the tunnel-like mesopore is formed radially by nano-drilling process. The size of the porous filamentous nanocarbon can be controlled according to the size of the nano-drilling catalyst and non-drilling conditions.

TECHNICAL FIELD

The present invention relates to a porous filamentous nanocarbon wheremesopores are formed on an outer periphery thereof, and moreparticularly, to a porous filamentous nanocarbon in which the mesoporesare radially formed from an outer periphery toward a fiber axis thereofalong an arrangement direction of a carbon hexagonal plane.

BACKGROUND ART

As researches for porous materials with porosity are actively conductedrecently, methods for manufacturing them are well known to the public.In particular, with regard to a method for manufacturing an activatedcharcoal and an activated carbon fiber and a method for manufacturing afibrous nanocarbon and a carbon nanotube using a metal catalyst, anumber of patents and theses are widely known. Herein, the carbonnanotube is a hollow carbon nanotube of which the diameter is 80 nm orless.

According to such a general activation method, a porous carbon material,which is typically called an activated carbon, is formed by formingplenty of micropores on the surface of the carbon material.

Two methods for manufacturing the activated charcoal and the activatedcarbon fiber are well known to the public. One is a method in which acarbon-based material undergoes a heat treatment at a temperature in arange of 300° C. to 1,100° C. for a pre-determined time in an ambient ofwater vapor, air, carbon dioxide, or the like, to thereby manufacturethe activated charcoal and the activated carbon fiber. The other one isa method in which a heat treatment is performed over the carbon-basedmaterial at a temperature in a range of 300° C. to 1,100° C. for apredetermined time in a salt having an alkali metal such as potassiumhydroxide, sodium hydroxide, or the like, and a separate rinsing and adrying process are sequentially performed so as to fabricate theactivated charcoal and the activated carbon fiber.

In the International Patent Publication No. WO8603455, filed on 1986 byHyperion Catalytic International Inc. in U.S.A., there has beenannounced a technology for a carbon nanotube with a hollow tubularstructure of which a fiber diameter is in a range of 3.5 nm to 70 nm,where a carbon hexagonal plane is concentrically arranged along a fiberaxis. The carbon nanotube is mainly classified into a single wall carbonnanotube (SWNT) in which a carbon hexagonal plane is configured with onesheet of a single wall, and a multi wall carbon nanotube (MWNT)configured with multi-walls. It becomes generally known that the fiberdiameter of the SWNT ranges from 0.4 nm to 3.5 nm, and the fiberdiameter of the MWNT ranges from 2.5 nm to 50 nm.

It is widely known a method for manufacturing a filamentous nanocarbonby thermally decomposing carbon monoxide and hydrocarbon gas as a carbonsource upon a metal catalyst. For example, U.S. Pat. No. 4,565,683discloses a method for manufacturing a filamentous carbon, where a fiberis formed in 1

long or greater by thermally decomposing carbon monoxide and hydrocarbonor the like at 540-800° C. using a catalyst such as iron oxide, iron,nickel, etc. In addition, Baker and Rodriguez et al. have announced amethod for manufacturing a carbon nanofiber of which surface area is ina range of 50

/g to 800

/g, by thermally decomposing hydrocarbon at 500˜700° C. using a catalystsuch as iron, nickel, cobalt, etc. Furthermore, Boehm et al. andMurayama and Rodriguez et al. have announced a method for manufacturinga filamentous nanocarbon by thermally decomposing hydrocarbon using atransition metal such as iron, cobalt, nickel, or alloy catalyst thereof(Bohem, Carbon, 11, 583 (1973); H. Murayama, T. Maeda, Nature, 245, 791;Rodriguez, N. M., 1993, J.Master.Res. 8(3233)).

Among various carbon nanofibers, there are a carbon nanofiber with aplatelet structure in which the carbon hexagonal plane is arrangedperpendicular to the fiber axis, and a carbon nanofiber with aHerringbone structure in which the carbon hexagonal plane is inclinedwith respect to the fiber axis at 20˜80° (Rodriguez, N. M., 1993,J.Master.Res. 8 (3233)). They do not have hollows therein, which is asignificant difference from the nanotube. FIGS. 1 a, 1 b and 1 c aretransmission electron microscope (TEM) images illustrating a carbonnanotube, a platelet filamentous nanocarbon, and a herringbonefilamentous nanocarbon, respectively. Since all the activated charcoal,the carbon nanotube, and the filamentous nanocarbon have large surfacearea, they may be applied to an adsorbent or a catalyst support. Becausethey have micropores of which sizes are 2 nm or smaller, they areeffective for adsorbing small-size molecules such as a gas detrimentalto an environment, a halogenated hydrocarbon contaminating water, or thelike. Therefore, they may be applied to a removal of a contaminantcaused by the exhaust gas of a factory, a purification of drinkingwater, and so forth. However, it is difficult to apply them to anadsorbent for a polymer, or a catalyst support for converting polymermaterial such as petroleum. In order that the activated charcoal, thefilamentous nanocarbon, etc, may be applied to these cases, it isnecessary to manufacture an absorbent having mesopores of which sizesare very uniform with low cost, wherein the size of the mesopore is in arange of 2 nm to 100 nm.

Several technologies for forming mesopores have been well known to thepublic.

According to one technology, a material that contains a removablemoiety, of some sizes, is polymerized so as to incorporate the moietyinto a solid product. The moiety is removed, leaving a porous solidhaving pores. For example, if firing a polymer mixed with an organicmaterial and an inorganic material, the organic material is burnt out sothat there occurs a fine pore in the inorganic material, of which sizeis correspondent to that of the organic material. The resultant poroussolid can have a very narrow pore size distribution in the mesoporerange, however, the preparation of such materials is very expensive andtime consuming.

Recently, a research result for synthesizing a material having mesoporesusing silica and silica alumina has been published, which is referred toas MCM-41 and M41-S disclosed in U.S. Pat. No. 5,108,725 and U.S. Pat.No. 5,378,440. However, because this is electrically an insulator and isvery unstable in alkali solution, it is not adaptive for applying it toa fuel cell, a battery, an electrolysis battery, capacitor, etc.

Another technology is related to a synthesis of a carbon materialselectively having mesopores therein. In detail, a polymer as a carbonsource is injected into a template such as zeolite, alumina, silica, andso forth, having mesopores therein. Alternatively, a pyrolytic carbon ischemically deposited on the template from hydrocarbon gas. Thereafter,the template is removed using fluoric acid or the like. However, thismethod has also disadvantages that its fabrication cost is too high, andproductivity is too poor in consideration of fabrication period andproduction amount.

Meanwhile, since most of the solid with the mesopores fabricated by theabove methods has a particulate shape, it has difficulties in filteringdespite the advantage of having high specific surface area.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a porous filamentous nanocarbon includinga filamentous nanocarbon having mesopores of which porosity is high andeach pore size is uniform, in which the size of the mesopore is in arange of 20 nm to 30 nm, and a method for manufacturing the same.

The present invention also provides a porous filamentous nanocarbon foran absorbent for separating a polymer such as protein or the like, achromatography material, an electrode material for a fuel cell,electrochemical reaction, and so forth, and a method for manufacturingthe same.

The present invention further provides a porous filamentous nanocarbonfor removing inconvenience for treatment thereof, by forming a solidwith mesopores in a filamentous shape of which the diameter is severalnanometers, not forming the solid with mesopores in a particulate shape,and a method for manufacturing the same.

Technical Solution

Embodiments of the present invention provide porous filamentousnanocarbons having a mesopore, wherein the mesopore is a tunnel-likepore which is radially formed from an outer periphery of the filamentousnanocarbon toward the central axis of the filamentous nanocarbon.

In some embodiment, the filamentous nanocarbon is a nanocarbon with aplatelet structure in which carbon hexagonal planes are verticallystacked with respect to the central axis. Alternatively, the filamentoushexagonal plane is a nanofiber with a Herringbone structure which isformed in the V-shape as being inclined at an angle in a range of 20 to80° with respect to the central axis. Herein, the mesopore is formedalong the arrangement direction of the carbon hexagonal planes.

In other embodiments, the filamentous nanocarbon has the diameter in arange of 2 to 100 nm, e.g., preferably in a range of 10 to 200 nm, andan aspect ratio of 4 or higher, e.g., preferably 10 or higher. Themesopore has the size in a range of 2 to 100 nm, e.g., preferably in arange of 2 to 30 nm, and the porosity of at least 20% or greater, e.g.,preferably 50% or greater.

In further embodiments of the present invention, there are providedmethods for forming a porous filamentous nanocarbon, the methodincluding radially forming a tunnel-like mesopore from an outerperiphery toward the central axis of a filamentous nano carbon byattaching a material having a metal catalyst on an outer periphery ofthe filamentous nanocarbon and removing a carbon hexagonal plane throughgasification in virtue of the metal catalyst.

In further other embodiments, the mesopore is formed according as apredetermined portion of the filamentous nanocarbon on which the metalcatalyst is attached selectively reacts with the metal catalyst.Accordingly, the predetermined portion of the carbon hexagonal plane isremoved, and the mesopore is formed along the arrangement direction ofthe carbon hexagonal plane. Because of the selective reaction, it ispossible to control the size of the tunnel-like mesopore and theporosity according to the size of the metal catalyst attached on thefilamentous nanocarbon or nano-drilling conditions.

Thus, since the nano-sized mesopore of which the diameter is in a rangeof 2 nm to 30 nm is formed on the outer periphery of the filamentousnanocarbon, the porous filamentous nanocarbon may be applied to theseparation/absorption of protein, petroleum, and so forth, and anelectrode for a fuel cell.

ADVANTAGEOUS EFFECTS

According to the present invention, it is possible to obtain a porousfilamentous nanocarbon having mesopores of which porosity is high andeach pore size is uniform, in which the size of the mesopore is in arange of 20 nm to 30 nm. This porous filamentous nanocarbon may bevariously applied to an adsorbent, a chromatography material, a catalystsupport, etc. Meanwhile, it is possible to more enhance the conductivitybetween particles in virtue of a filamentous shape when applying theinventive nanocarbon to electrochemical applications requiringconductivity. In addition, the present invention provides anadvantageous merit of removing inconvenience for treatment thereof,e.g., filtering, because a solid with mesopores has a filamentous shapeof which the diameter is several nanometers instead of a particulateshape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a transmission electron microscope (TEM) images showing afilamentous nanocarbon having a tubular structure;

FIG. 1 b is a TEM showing photographs a filamentous nanocarbon having aplatelet structure;

FIG. 1 c is a TEM images showing a filamentous nanocarbon having aHerringbone structure;

FIG. 2 is a schematic view and TEM images illustrating a filamentousnanocarbon with a tubular structure according to the present invention;

FIG. 3 is a schematic view and TEM images illustrating a filamentousnanocarbon with a platelet structure according to the present invention;

FIG. 4 is a schematic view and TEM images illustrating a filamentousnanocarbon with a Herringbone structure according to the presentinvention;

FIG. 5 is a schematic view and TEM images illustrating a filamentousnanocarbon in which mesopores are formed by nano-drilling according tothe present invention;

FIGS. 6 to 9 are TEM images illustrating a filamentous nanocarbon inwhich mesopores are formed by nano-drilling process according to thepresent invention; and

FIG. 10 is a graph illustrating electrochemical activity in comparisonof the filamentous nanocarbon according to the present invention withthe prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 are high resolution transmission electron microscope (TEM) imagesshowing conventional filamentous nanocarbons having three representativestructures such as a tubular structure, a platelet structure, and aHerringbone structure, respectively, and also illustrates typical2-dimensional models corresponding to the respective structures.

FIGS. 2 to 4 illustrate that the filamentous nanocarbons with the threestructures are formed by finely stacking nano-rods, which are structuralunits. That is, a tunnel-like mesopore according to the presentinvention is formed based on a new structure of a filamentous nanocarbonconfigured with the stacked carbon nano-rods.

The nano-rod, which is a basic unit constituting the filamentousnanocarbon, has a structure where fullerene tubes are overlapped alongthe same axis and one end thereof is closed, wherein the fullerene tubecluster is configured as a cylindrical shape such that carbon hexagonalplanes are overlapped with each other (refer to FIG. 3 a). In general,the nano-rod is configured as a hexagonal prism having 4˜6 number ofcoaxes, of which each diameter is about 2.5 nm and each size is in arange of 20 nm to 80 nm. Detail descriptions for the nano-rod aredisclosed more fully in the thesis of S.-H. Yoon et al. (S.-H. Yoon, S.Lim, S.-h. Hong, I. Mochida, B. An, K. Yokogawa. 2004, Carbon, 42(15),3087-3095; B. An, K. Yokogawa, S. Lim, S.-H. Yoon, I. Mochida. In:Carbon 2004 International Conference, Brown University: RI (USA), 2004).

In the present invention, nano-sized mesopores are formed on an outerperiphery of the filamentous nanocarbon using a nano-drilling process.If a nano catalyst is attached on the outer periphery of the filamentousnanocarbon, and then a heat treatment is performed over the filamentousnanocarbon on which the nano catalyst is attached in hydrogen or oxygenambient, there occurs a hydrogenation or an oxidation gasificationreaction so that there is formed a tunnel penetrating from the outersurface into an interior, of which a size is corresponding to that ofthe nano catalyst. A drilling pattern formed by the inventive method isnot random in comparison with the prior art, but is uniformly formedalong the arrangement direction of the carbon hexagonal plane.Accordingly, the nano catalyst under hydrogenation or oxidation ambientremoves the filamentous nanocarbon from a portion on which the nanocatalyst is attached along the stacked structure of the nano-rods, tothereby form the nano tunnels by drilling the filamentous nanocarbon.Referring to FIG. 5, it is shown that the predetermined portion of thenano-rod is removed and thus the tunnel is formed.

This reaction is caused by gasification of the metal with respect tocarbon due to hydrogen, oxygen, or the like. The reason the mesopore isformed in a shape of the tunnel is that the decomposition of the carbonplane due to the gasification occurs along the alignment direction ofthe nano-rod units, which are formed as a hexagonal prism of the carbonhexagonal plane, because the surface forming sidewalls of the carbonhexagonal plane is more reactive than the base surface. Accordingly, thenano-drilling reaction progresses along a major axis of the nano-rodfrom the outer periphery of the filamentous nanocarbon to the center ofthe fiber. This is possible by preferentially gasifying and removing thenano-rods where the catalyst is attached on an end thereof in hydrogenor oxygen ambient. At this time, since one or more nano-rods may reactwith reaction gas by means of the catalyst, there is formed the nanotunnel of which width is 2˜30 nm greater than the diameter of thenano-rod. Therefore, there are formed the tunnel shaped mesoporesradially along the alignment axis of the nano-rods from the outerperiphery toward the center of the fiber.

The metal catalyst for nano-drilling, i.e., gasification, may employ anelement in the groups V, VI, VII, and

of the periodic table. Preferably, the catalyst is iron (Fe), cobalt(Co), nickel (Ni), molybdenum (Mo), vanadium (V), chromium (Cr),platinum (Pt), palladium (Pd), ruthenium (Ru), copper (Cu), silver (Ag),zinc (Zn), tin (Sn), and an alloy thereof. It is preferable that thealloy catalyst employ Ni—Cu, Fe—Ni, Fe—Pt, Fe—Mo, Ni—Mo, Co—Mo, Pt—Ru,etc. It is preferable that the size of the catalyst be in a range of 2nm to 50 nm. In case of too small, there occurs micropores. On thecontrary, in case of too large, a great amount of the filamentousnanocarbon may be removed.

It is preferable that the reaction gas for activation employs hydrogengas or oxygen gas. Furthermore, carbon dioxide (CO₂) gas, sulfur dioxide(SO₂) gas, nitrogen monoxide (NO) gas, nitrogen dioxide (NO₂) gas, andwater may be used as the reaction gas. If the reaction conditions arenot appropriately controlled in the activation process, the graphitelayer of the nano-rod may be melt or be inserted into an intermediate sothat it is very important to adjust the process temperature. Forinstance, it is preferable to perform the activation process at400˜1,200° C., more preferably at 500˜900° C., in case of hydrogenation.In addition, it is preferable to perform the activation process at100˜500° C., more preferably at 200˜400° C., in case of oxidation.

MODE FOR THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. However, the present invention is not limited to theembodiments illustrated herein after, and the embodiments herein arerather introduced to provide easy and complete understanding of thescope and spirit of the present invention.

To begin with, a method for manufacturing a filamentous nanocarbon usedin the present invention will be set forth in brief herebelow.

First, a method for manufacturing a filamentous nanocarbon with atubular structure will be illustrated. First of all, Fe/Ni alloy used asa metal catalyst is fabricated as a following method. A nickel nitrideand an iron nitride are dissolved in distilled water at roomtemperature. Next, ammonium bicarbonate is added and stirred.Precipitate produced from this solution is washed with distilled waterand ethanol, and then is dried in vacuum state. The dried precipitate isfired at 400° C. in dry air ambient so as to fabricate Fe—Ni oxide. TheFe—Ni oxide is reduced at 400° C. in H₂/He ambient. Thereafter, anaftertreatment is processed again at room temperature in O₂/He ambientto thereby obtain Fe—Ni alloy catalyst. The catalyst fabricated by thismethod is put into a quartz tube in a reaction furnace. Afterwards, aheat treatment is performed at 625° C. for 2 hours in H₂/He ambient.Thereafter, a heat treatment is performed at 625° C. for 2 hours whileinflowing mixture gas of CO/H₂, to thereby obtain a carbon fiber.

The fabricated carbon fiber has such a structure that a carbon hexagonalplane is parallel with a fiber axis and a hollow exists therein. (FIG.2). The outer diameter of the fiber is in a range of 5 to 35 nm, and anaspect ratio is 30 or higher. FIG. 2 a is a TEM image, and FIG. 2 b isan illustrative view setting forth a stacked structure of nano-rods.FIGS. 2C and 2D are scanning tunneling microscope (STM) images of thesurface of the fiber. It is possible to observe that the nano-rods areinterconnected and stacked from the drawings.

Second, a method for manufacturing a filamentous nanocarbon with aplatelet structure will be illustrated. After fabricating an Fe catalystfrom iron nitride using the aforementioned method, the Fe catalyst isput into the quartz tube in the reaction furnace. Thereafter, a heattreatment is performed at 600° C. for 2 hours while inflowing mixturegas of CO/H The fabricated carbon fiber has the platelet structure wherethe carbon hexagonal plane is stacked perpendicular to the fiber axis(FIG. 3).

The outer diameter of the fiber is in a range of 90 nm to 300 nm, and anaspect ratio is 30 or higher. FIGS. 3 a and 3 b are TEM images and FIG.3 c is an STM image of the surface of the nanocarbon. FIG. 3 d is anillustrative view setting forth a stacked structure of nano-rods. It ispossible to observe that the nano-rod is stacked perpendicular to thefiber axis from the drawings.

Third, a method for manufacturing a filamentous nanocarbon with aHerringbone structure will be illustrated. After fabricating a Ni—Cualloy catalyst from nickel nitride and copper nitride using theaforementioned method, the Ni—Cu alloy catalyst is put into the quartztube in the reaction furnace. Thereafter, a heat treatment is performedat 580° C. for 2 hours in H₂/He ambient while inflowing mixture gas ofethylene/hydrogen so as to obtain a carbon fiber. The fabricated carbonfiber has such a Herringbone structure that the carbon hexagonal planeis formed in the V-shape with respect to the fiber axis at an angle of20˜80° (FIG. 4). The outer diameter of the fiber is in a range of 80 nmto 350 nm, and an aspect ratio is 30 or higher. FIGS. 4 a and 4 b areTEM images and FIG. 4 c is an STM image of the surface of the fiber.FIG. 4 d is an illustrative view setting forth a stacked structure ofnano-rods. It is possible to observe that the nano-rod is stacked asbeing inclined with respect to the fiber axis at a predetermined anglefrom the drawings.

Next, there will be illustrated a method for manufacturing a porousfilamentous nanocarbon using a nano-drilling process of the presentinvention herebelow.

EMBODIMENT 1

The nickel particle used for a nano-drill catalyst is attached on theouter periphery of the Herringbone filamentous nanocarbon by dipping anddispersing the Herringbone filamentous nanocarbon in nickel nitridesolution. The filamentous nanocarbon is vacuum dried at 150° C. tofabricate a nanofiber on which the nickel catalyst is attached. Thefilamentous nano-carbon is put into the quartz tube in the reactionfurnace. Thereafter, a heat treatment is performed at 800° C. for 2hours in mixture gas of H₂/He ambient.

The fabricated porous filamentous nanocarbon, as illustrated in a TEMimage in FIG. 6, becomes a very porous nanofiber in which the nanotunnels are formed. The nano tunnel is formed along the arrangementdirection of the carbon hexagonal plane without any change in thestructure of the filamentous nanocarbon. The nano tunnel has a diameterin a range of 5 to 30 nm. The specific surface area and a volume of themesopore are measured to be 352

/g and 0.42

/g, respectively, using ₂NB runauer-Emitter-Teller (BET) method.

EMBODIMENT 2

The nickel particle used for a nano-drill catalyst is attached on theouter periphery of the Herringbone filamentous nanocarbon by dipping anddispersing the Herringbone filamentous nanocarbon in nickel nitridesolution. The filamentous nanocarbon is vacuum dried at 150° C. tofabricate a nanofiber on which the nickel catalyst is attached. Thefilamentous nano-carbon on which the nickel catalyst is attached is putinto the quartz tube in the reaction furnace. Thereafter, a heattreatment is performed at 350° C. for 3 hours in O₂ ambient.

The fabricated porous filamentous nanocarbon, as illustrated in a TEMimage in FIG. 7, becomes a very porous nanofiber in which the nanotunnels are formed. The nano tunnel is formed along the arrangementdirection of the carbon hexagonal plane without any change in thestructure of the filamentous nanocarbon. The nano tunnel has a diameterin a range of 2 to 10 nm. Herein, although the average size of themesopore is smaller than that of the first embodiment, the mesopores areuniformly distributed in comparison with the first embodiment. Thespecific surface area and a volume of the mesopore are measured to be298

/g and 0.39

/g, respectively, using ₂N BET method.

EMBODIMENT 3

Iron particles used for a nano-drill catalyst are attached on the outerperiphery of the Herringbone filamentous nanocarbon by dipping anddispersing the Herringbone filamentous nanocarbon in iron nitridesolution. The filamentous nanocarbon is vacuum dried at 150° C. tofabricate a nanofiber on which the iron catalyst is attached. Thefilamentous nano-carbon on which the iron catalyst is attached is putinto the quartz tube in the reaction furnace. Thereafter, a heattreatment is performed at 850° C. for 3 hours in mixture gas of He/H₂ambient.

The fabricated porous filamentous nanocarbon, as illustrated in a TEMimage in FIG. 8, becomes a very porous nanofiber in which the nanotunnels are formed. The nano tunnel is formed along the arrangementdirection of the carbon hexagonal plane. However, since a graphitizationpartially occurs at the same time with the gasification due to thecatalyst unlike the first and second embodiments, a carbon structurearound the mesopore is slightly changed so as to fabricate a porousmaterial having good graphitizability around the mesopore. The specificsurface area and a volume of the mesopore are measured to be 254

/g and 0.33

/g, respectively, using ₂NBET method.

EMBODIMENT 4

The nickel particle used for a nano-drill catalyst is attached on theouter periphery of the platelet filamentous nanocarbon by dipping anddispersing the platelet filamentous nanocarbon in nickel nitridesolution. The filamentous nanocarbon is vacuum dried at 150° C. tofabricate a nanofiber on which the nickel catalyst is attached. Thefilamentous nano-carbon on which the nickel catalyst is attached, is putinto the quartz tube in the reaction furnace. Thereafter, a heattreatment is performed at 800° C. for 3 hours in mixture gas of H₂/Heambient.

The fabricated porous filamentous nanocarbon, as illustrated in a TEMimage in FIG. 9, becomes a very porous nanofiber in which the nanotunnels are formed. The nano tunnel is formed along the arrangementdirection of the carbon hexagonal plane without any change in thestructure of the filamentous nanocarbon. The nano tunnel has a diameterin a range of 6 to 32 nm. The specific surface area and a volume of thepore are measured to be 154

/g and 0.24

/g, respectively, using ₂NBET method.

COMPARATIVE EXAMPLE 1

In the first comparative example, a conventional alkali cactivationmethod is applied to the Herringbone filamentous nanocarbon. A mixtureof the Herringbone filamentous nanocarbon and KOH (nanocarbon:KOH=1:4w/w) is put on a pan. Thereafter, a heat treatment is performed at 850°C. for 2 hours in mixture gas of H₂/He ambient.

From a TEM image, it is observed that predetermined portions of thecarbon hexagonal plane are removed at a regular space, forming a laddershape. According to the BET result, it is understood that micropores ofwhich specific surface area and size are 154

/g and 1.0 nm, respectively, are formed. Therefore, it is known that theconventional alkali cactivation method is not adaptive for selectivelyforming mesopores of the inventive porous filamentous nanocarbon.

COMPARATIVE EXAMPLE 2

The nickel particle used for a nano-drill catalyst is attached on theouter periphery of the Herringbone filamentous nanocarbon by dipping anddispersing the filamentous nanocarbon with butte structure in nickelnitride solution. The filamentous nanocarbon is vacuum dried at 150° C.to fabricate a nanofiber on which the nickel catalyst is attached. Thefilamentous nano-carbon on which the nickel catalyst is attached is putinto the quartz tube in the reaction furnace. Thereafter, a heattreatment is performed at 800° C. for 3 hours in mixture gas of H₂/Heambient.

Unlike the embodiments, it is known that the filamentous nanocarbon ofthe second comparative example shows a weight change before and afterthe reaction is less than 5%. This is well observed in the TEM imagethat the micropores are not formed uniformly. The specific surface areaand a volume of the pore are measured to be 122

/g and 0.21

/g, respectively, using ₂NBET method. Thus, it is known that theinventive nano-drilling method is not effective for a tubularfilamentous nanocarbon, i.e., the carbon nanotube. As the result of thesecond comparative example, considering that the nano-drilling method isnot effective for the tubular structure in which the end portion of thenano-rod is not exposed, the fabrication of the tunnel-like mesoporesaccording to the nano-drilling of the present invention is performedsuch that the catalyst attached on the exposed end portion of thenano-rod deems to selectively gasify the nano-rods therearound.

COMPARATIVE EXAMPLE 3

The nickel particle used for a nano-drill catalyst is attached on acarbon black by dipping and dispersing the carbon black in nickelnitride solution. The carbon black is vacuum dried at 150° C. tofabricate the carbon black on which the nickel catalyst is attached. Thecarbon black on which the nickel catalyst is attached on is put into thequartz tube in the reaction furnace. Thereafter, a heat treatment isperformed at 800° C. for 3 hours in mixture gas of H₂/He ambient.

There is little weight change before and after the reaction, and thus itis known that the nano-drilling method according to the presentinvention is not effective for the carbon black.

Examples in which the porous filamentous nanocarbon fabricated by thenano-drilling method of the present invention is applied will beillustrated herebelow.

First, the porous filamentous nanocarbon can be applied to an adsorbentand a chromatography. Since the mesopore of the porous filamentousnanocarbon according to the present invention has a maximum pathway ofabout 200 nm long, it takes about 2 seconds for molecules to diffusefrom one end of the mesopore to the other end. In this manner, thediffusion time is very short so that it is very effective for theinventive nanocarbon to be applied to the adsorbent and thechromatography. In particular, in case of the chromatography, it is veryadaptively used for separating biologically important molecules such asenzyme, steroid, alkaloid, hormone, protein, and so forth.

Second, the porous filamentous nanocarbon can be applied to a catalystsupport. Due to the short diffusion pathway as described above, it maybe importantly applied to the conversion of the polymer material, e.g.,synthesis of steroid and enzyme, refinement of petroleum, or the like.

Third, the porous filamentous nanocarbon can be applied to an electrodefor electrochemical reaction. The filamentous nanocarbon according tothe present invention is dipped into the catalyst metal solution and iscoated with the catalyst metal, to thereby form an electrode on thesurface of the porous filamentous nanocarbon. Since the material sofabricated is resistant to alkali or acid, it is possible to apply theinventive nanocarbon to electrochemical reaction requiring severeenvironments. For instance, the coated Pt-Ru catalyst may be used as acatalyst for oxidizing methanol in methanol fuel cell. FIG. 10 is acyclic voltammogram illustrating methanol oxidation using Pt—Ru catalystelectrode and Ag/AgCl electrode, which shows an activity measured in thepreset invention about two times greater than the prior art.

INDUSTRIAL APPLICABILITY

The porous filamentous nanocarbon of the present invention may bevariously applied to an adsorbent, a chromatography material, a catalystsupport, etc. That is, it is possible to apply the porous filamentousnanocarbon to the separation/absorption of protein, petroleum, and soforth, and an electrode for a fuel cell.

1. A porous filamentous nanocarbon having a mesopore, wherein themesopore is a tunnel-like pore which is radially formed from an outerperiphery of the filamentous nanocarbon toward the central axis of thefilamentous nanocarbon.
 2. The porous filamentous nanocarbon of claim 1,wherein the filamentous nanocarbon is a nanocarbon with a plateletstructure in which carbon hexagonal planes are vertically stacked withrespect to the central axis, the mesopore being formed along thearrangement direction of the carbon hexagonal planes.
 3. The porousfilamentous nanocarbon of claim 1, wherein the filamentous hexagonalplane is a nanofiber with a Herringbone structure which is formed in theV-shape as being inclined at an angle in a range of 20 to 80° withrespect to the central axis, the mesopore being formed along thearrangement direction of the carbon hexagonal planes.
 4. The porousfilamentous nanocarbon of anyone of claims 1 to 3, wherein thefilamentous nanocarbon has the diameter in a range of 2 to 100 nm, andan aspect ratio of 4 or higher.
 5. The porous filamentous nanocarbon ofanyone of claims 1 to 3, wherein the mesopore has the size in a range of2 to 100 nm, and the porosity of at least 20% or greater.
 6. A methodfor forming a porous filamentous nanocarbon, the method comprisingradially forming a tunnel-like mesopore from an outer periphery towardthe central axis of a filamentous nano carbon by attaching a materialhaving a metal catalyst on an outer periphery of the filamentousnanocarbon and removing a carbon hexagonal plane through gasification invirtue of the metal catalyst.
 7. The method of claim 6, wherein themetal catalyst includes at least one selected from the groups V, VI,VII, and

of the periodic table.
 8. The method of claim 7, wherein the metalcatalyst is at least one selected from the group consisting of iron(Fe), nickel (Ni), copper (Cu), platinum (Pt), manganese (Mn), vanadium(V), and an alloy thereof.
 9. The method of claim 6, wherein themesopore is formed according as a predetermined portion of thefilamentous nanocarbon on which the metal catalyst is attached isremoved through a selective gasification reaction in virtue of the metalcatalyst.
 10. The method of claim 9, wherein the mesopore is formedalong the arrangement direction of the carbon hexagonal plane as thepredetermined portion of the carbon hexagonal plane on which the metalcatalyst is attached is removed through the selective gasificationreaction.
 11. The method of claim 6, wherein a reactant for gasifyingthe carbon hexagonal plane in virtue of the metal catalyst includeshydrogen gas.
 12. The method of claim 11, wherein the gasificationtemperature is in a range of 500° C. to 900° C.
 13. The method of claim6, wherein a reactant for gasifying the carbon hexagonal plane in virtueof the metal catalyst includes oxygen gas.
 14. The method of claim 13,wherein an activation temperature is in a range of 200° C. to 400° C.